Disappointing News For Dogs -- and People

A major study of the joint supplements glucosamine and chondroitin found they offer no benefit to arthritic joints.

An analysis of ten large studies testing the effect of glucosamine or chondroitin on arthritis finds that neither one reduces pain or the narrowing that occurs in arthritic joints.

Chondroitin and glucosamine supplements have been recommended in some arthritis treatment guidelines, prescribed by general practitioners and rheumatologists and used by many patients and their pets as over-the-counter medications to improve symptoms of arthritis. Global sales of glucosamine were nearly $2 billion in 2008.

The researchers found no statistical evidence that either type of preparation reduced the pain of arthritis. They also found no X-ray evidence that these preparations increased the space between joints.

Glucosamine is a small molecule and chondroitin sulfate is an extremely large one. Large amounts of both are found in the cartilage of joints and in the synovial fluid which lubricates these joints. Since arthritis is a degenerative disease of the joints, it seems reasonable that either compound could aid in the repair of damaged joints. Some studies have found short-term evidence of this; others have found none at all.

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The current study, published online by the British Medical Journal (BMJ) last week, comes down clearly on the side of "not helpful."

Joints are areas where bones connect to each other, such as at the hip and the knee. The bones do not meet; structures called ligaments connect one bone with another. Ligaments are largely made up of cartilage, a tough, elastic tissue. As a person ages, these ligaments tend to shrink, lose their elasticity and become frayed. This is part of what causes the pain of arthritis.

In the current study, the researchers performed a statistical analysis of the combined results of previous trials where subjects with knee or hip arthritis took either glucosamine or chondroitin sulfate. The researchers included only trials that were controlled (compared a treatment against a placebo) and had at least 100 subjects in each treatment group. They evaluated 10 such trials, with 3,803 total participants: six trials that tested the effects of a glucosamine preparation, three that tested chondroitin sulfate and one which tested both preparations.

The researchers found no statistical evidence that either type of preparation reduced the pain of arthritis. They also found no X-ray evidence that these preparations increased the space between joints. Narrowing of the space between the bones that make up a joint is an indication of arthritis, and some previous studies have found glucosamine or chondroitin sulfate to increase this space.

The researchers note that, just as they make statistical criticisms of some previous studies, other researchers may criticize their study, using the argument that they "have not compared like with like." Often (but not always), when researchers make statistical criticisms of other studies, they are arguing about whether an effect is a small effect or no effect at all. When a large effect is seen in a study, it generally withstands various types of statistical treatment and is obvious even without any statistical treatment at all.

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There is no question that some arthritis sufferers have taken glucosamine or chondroitin supplements and reported feeling better afterwards. There are many possible reasons for this. It could be that these supplements are effective in a small amount of people. It could also be a placebo effect: simply doing something for a condition may make people feel better than doing nothing at all. Taking a pill for arthritis may give arthritis sufferers hope, and that in itself may translate into feeling better.

The study researchers (and many other researchers) point out that taking either glucosamine or chondroitin sulfate is not dangerous. That's more than can be said for many supplements that are sold today. People who take glucosamine or chondroitin supplements do not appear to be taking any health risk. But the study finds no reason to take them.

An article on the study was published online by the British Medical Journal (BMJ) on September 16, 2010.